EM Waves, Interference, Intensity

1. The problem statement, all variables and given/known data
Q1 and 3 in this file:
http://phstudy.technion.ac.il/~sm114075/sm09/Documents/Physics2mm_Hw7.pdf" [Broken]
(I get how to do Q2)2. Relevant equations

basic EM, Interference and Intensity related equations, I guess.

3. The attempt at a solution

Well, for Q1 I would want to get some sort of expressions for each of the waves, of the form Acos(wt-kr) and then figure it out from there. Thing is - the size of k is a given parameter (it says I can set the wavelength) but how can I figure out its direction?

For Q3 I'm completely lost. There's an equation for Intensity involving only the wave formula normed and squared - Would the best thing to do is add the two waves to one function, calculate its norm and square it? Is there a nicer option?